Minerals have fascinated David Friend ever since he came across mica and quartz on a construction site as a kid. Now visitors of all ages can marvel at giant gems at the Yale Peabody Museum of Natural History’s recently unveiled David Friend Hall, home to more than $50 million in gems and minerals. We paid a visit to the Boston philanthropist and Yale alum’s Back Bay apartment to see his personal treasure trove and learn more about what the 2,300-square-foot gallery has to offer.

There aren’t too many signs in the exhibit hall. What’s the thinking behind that approach? Academic museums particularly always seem to want to teach something. …. [But] people gravitate toward the few big, flashy pieces in the room. I wanted something that would inspire kids to want to learn more, because if kids want to learn something, they’ll learn it. You’ve got to have the equivalent of that 80-foot brontosaurus at Yale. When you look at them, they’re just like, “I cannot believe that somebody pulled that out of the ground.”

The showstoppers include your giant amethyst geode. How did it come to be in your collection? I talked to the guy who mined that. When they found the thing, they would drill a small whole in it and stick in one of those scopes—you know, that doctors use to look at your organs—and look around inside to see what’s there before they start cutting. Ninety-nine percent of the time, it’s nothing really spectacular, but every now and then they find a geode like that one that’s just awe-inspiring to look at—beautiful dark purple crystals and this big, sparkly white calcite crystal. It was on the back of a truck in the mineral show in Tucson. Some friend of mine called me up: “Dave, you need to get down here right away.” This guy had a truckload of stuff he had brought from Brazil and Uruguay. I saw it and negotiated and bought it right there in the back of the truck.

You also contributed a 30-million-year-old sandstone concretion. Where did it come from? There’s a sand quarry in Fontainebleau that’s been mined for its very pure white silica sand since the Middle Ages. It had been used to make the stained-glass windows in Notre Dame and all the great cathedrals in Europe. You know that glass pyramid at the Louvre? That’s also made from this sand from this quarry. It’s still being used. About 30 years ago, they were digging down at the bottom, and they struck these solid objects.

What about the smaller pieces? The mineral world has gotten to be like the art world. Pieces are so expensive that museums can’t afford to buy any of these things anymore. There’s maybe a hundred major collectors in the country that own all the best pieces. I went to the ones that I knew, not knowing whether this would work, and I said, “I’d like you to let us borrow the very best stuff in your collections.” To my surprise, everybody said yes. In fact, I had people who were mad at me because we didn’t have room for their pieces. But they’ll get their chance in the next go-around.